Kristin and Jill are selling fruit for a school fundraiser Customers can buy small boxes of

grapefruit and large boxes of grapefruit. Kristin sold 3 small boxes of grapefruit and 9 large

boxes of grapefruit for a total of $99. Jill sold 12 small boxes of grapefruit and 10 large boxes of

grapefruit for a total of $162. How much does one small box of grapefruit cost?